I assume that it's rationally to switch the broker in case it levies too big fees or spreads are too wide. The latter depends on the current market condition, pool of liquidity providers and so on.
As for the fees then I am for cost-effective brokers, which don't levy inactivity fees, swaps, and actually have no commissions, or at least offer accounts where you pay only the spread.
So if you realize that the biggest part of your deposit is eaten by commissions or other stuff, then think of changing the broker.