The misconception with LACP is that you get "aggregated bandwidth" all the time. This is not true. A single host connection will not see more than the single port speed. IF the host is 10G and the server is 40G, the host will never see more than 10G.
LACP allows for multiple clients to aggregate bandwidth. Again, no one host will ever use more than its' single fastest link to the server. I can have multiple hosts using those links.
So to answer your questions, if you create a 4-port (4 x 25Gb) 100Gb LACP port-channel, no client will ever see more than 25Gb of bandwidth (provided the client is using 25Gb and the connection is 25Gb end-to-end). I can using multiple clients that with any luck will ultimately saturate the multiple ports in the LACP port-channel.