While fishing small streams with a lot of cover, you won't be casting long distances. Your main concern is accuracy So, learning how to roll cast accurately in short distances is a benefit. Often in these streams trout will be hiding under cover such as a sunken log, roots, or an undercut bank. You'll probably have to get close to where the trout are to have any chance of getting your line to where they are - 10 to 20 feet, maybe.
If you're after trout below the surface, you must get your fly to sink quickly. Adding weight to your leader (split-shot, etc) will be necessary. This can make casting more difficult, but only if you let it. The weight on your leader can make it easier for you to feel the end of your leader & feel how far out your fly is traveling. If you feel it going out too far, you can adjust in mid-cast by pulling the line back towards you with your non-casting hand. Remember, you're roll casting only a very short distance. Having the weight on your leader can help you shoot the line out a little better on short roll casts, especially because you're not concerned with back casts or having the line in the air at all.
You may also have to use a "flick" or "switch" cast. This is a lot like a side-ways roll cast. For a downstream cast, if you stand facing the far bank,you essentially pull the line & wit the rod upstream. When you've pulled enough line in to make a cast, move your rod slightly in the downstream direction so that the line & rod form the shape of a "D" (or backward "D", depending on which direction the water is flowing). Then flick, or roll cast the line out to where you want it. This technique is especially useful on faster moving water in places where you can't get the line back in a good position for a regular roll cast. Remember, the line goes where you point the rod tip (hopefully), so stop the rod tip somewhere in front of you or you'll end up tangled in the bushes directly downstream from you. Practice this sideways roll casting on more open water first. It's very easy to tangle your line around your rod while performing this cast.
If you end up in spot where you can use a back cast, but are worried about getting your back cast through a tight opening in the trees, etc make sure you position your self correctly. You want the opening in the cover to be directly over the shoulder of your casting hand. Then, when making your back cast, make sure you send it directly over your shoulder. Keep your arm & wrist straight. You've got to be careful not to roll your rod away from your body on the back cast or you'll end up tangled in the trees along the stream bank behind you.
You might also find a part of the stream so tight & covered with growth that you can't even get to the bank to cast. Here you will have to hold your rod out, through, or over the bushes, etc at a steep angle & let your line down onto the water. You can "dap" or move your fly along the surface to fool active trout or simply allow the current to take your line down into the cover where the trout are feeding. Be careful if you do hook up with a fish. You'll need a way to land it. It's best to plan all this out before you put your line on the water!!
If you're fishing wide open streams with no obstacles (like those flowing through a pasture), roll casting might not even be an option for you. What you really have to concerned with in these situations is being spotted by the trout. Stay far away from the stream bank & keep a low profile. You might find yourself on one knee a few feet back from the stream bank casting towards the stream. In this position it's a neat trick to allow your cast to come down on both the water & the land between you & the stream. Of course, you can only do this if casting to a small spot of water, bringing your fly down right on top of a feeding fish. With some of your line laying on the ground in front of you, you'll have hardly any drift before before drag sets in. This is a good, fast action, dry fly method that is an absolute thrill if you hook a fish this way.
Overall, fishing on small streams forces you to get creative with your casting. You will get your line tangled in the bushes & trees, - even the best anglers do. But with creativity, practice, & patience it will happen less often.