Scouts are another must have Space Marine unit in my gaming experience, since they offer so much for the point cost.
They are a scoring unit, can take a variety of interesting wargear, infiltrate, outflank, and ride in a storm speeder.
The balance in using them is in understanding they are not power armored troops and rely on cover and positioning to keep them safe. And even though scouts can do a variety of things, you have to pick one primary role for each scout group in your army.
These two primary roles are often shooting based or assault based and work off infiltrating them or outflanking them.
Shooting based scouts work best with Telion (worth the upgrade IMHO) and sniper rifles in a supporting role. Infiltrate them into a good position on the table and use the sniper rifle to assign shots, take down high toughness models, and blast away with Telion- plus they are a scoring unit for later in the game. Camo cloaks are nice if you have the points but you can work around them by using terrain and having (and using) other units on the table so your opponent doesn’t have the time to shoot at the scouts.
The second is an assault based scout unit- taking in the maximum number with bolt pistols, close combat weapons, and a heavy bolter with shells, and a teleport homer (again for the deepstrike guide option if you have terminators).
These scouts CAN infiltrate and hide out if the terrain is there for later in the game or to be a nuisance to your opponent, or they can outflank to force your opponent to deal with them when they arrive- shooting that turn, and then if they are not dealt with assaulting the next turn. YES they are not dedicated shooting or assaulting units, but they have the versatility with the infiltrate and outflank to go up against similar units or units that are not dedicated in that way.