Followers in Skyrim can be very useful. Here are some tips on them:
You can provide them with better weapons and armor. However, they don’t always use the better weapons or wear the armor. For example, if a follower is specialised in light armor they usually will not wear heavy armor.
Is your inventory full and are you overencumbered? Drop the heavy stuff and ask your follower to pick it up. They will be able to carry enormous amounts that way.
When you are sneaking, it’s best to ask your follower to wait. It’s quite usual to see your follower sneak with heavy armor which will make enemies detect you. And often they will attack when you are not ready yet.