Internal sleeves keep your shovel and probe organized inside the main compartment rather than in a separate front-access pocket. They're typically found on streamlined or ultralight packs where saving weight and reducing bulk matter more than lightning-fast access. The tradeoff is speed — in an avalanche emergency, you'll need to open your main compartment and possibly dig past other gear to reach your probe and shovel, which costs precious seconds.
If you're an experienced backcountry rider who values a minimalist setup and practices regularly with your gear, an internal sleeve can work fine. Just be disciplined about packing so your avy tools are always on top and easy to grab. However, if you're newer to backcountry travel or want the safest, fastest option, a dedicated front pocket is the better choice.
Think of it this way: internal sleeves prioritize pack weight and clean design, while front pockets prioritize emergency speed. For most backcountry skiers and snowboarders, speed wins.