Tor introduced guards, which are - oversimplified said - relays the client picks and holds for some time as the first hop, to protect the client against the so-called 'predecessor attack'. Entry guards prevent the client from connecting to the majority of the network in a short amount of time.
Now there's some planning towards increasing the guard rotation period and reducing the number of guards a client picks for that time-frame.
How are fewer guards per client better then more guards? Why is a longer rotation period (a client sticks with its guards longer) beneficial for the client?