When you send or exchange assets Exodus only uses the the amount listed in "Available Balance". This balance can be different than your wallet balance for the following reasons:
Each time you send a blockchain asset you must include a tiny transaction fee to ensure your payment is processed and reaches the destination. These fees are paid to each assets network (Bitcoin, Ethereum, etc.) they are not kept by Exodus.
If the asset network is busy, which has been the case for Bitcoin since mid-2016, these fees are typically higher. You can always see the fee, along with the corresponding asset amount, in the lower right of the send dialog.
If you are looking to minimize transaction fees less popular networks have lower tranastion fees. Today Litecoin or Ethereum are less than Bitcoin.