FM tuners will "capture" a signal that is above a very low threshold (with modern tuners), and as long as your signal is above that capture level a stronger signal (less gain loss) doesn't matter. A splitter incurs a gain loss, but S/N ratio is unchanged. This is why signal booster amplifiers generally don't help. Signal-to-Noise ratio is usually more important than signal strength, and audiophile tuners generally have a front end superior to what you find in a booster amp. One possible exception to this rule is if the antenna is located a long way from the tuner, and the signal needs to be boosted so that it is not degraded by pickup in the leadin wire. In the days of unshielded twinlead, and in fringe reception areas (where I live) this was often the case, but nowadays shielded coax is the usual lead-in wire. I have about 100 feet of shielded 300 ohm twinlead, and it proved superior to a remote (at the antenna) booster amp.
To your question...a splitter may degrade reception of stations that are already so weak that they are unpleasant to listen to. For the stronger stations - the ones you are apt to listen to - there probably will be no degradation. Keep the antenna away from metalic stuff and wires. You may need to move the antenna around to experimentally find the best location/orientation. Maybe you don't remember "rabbit ears" TV antenna, but twisting those things around so as to optimize the TV picture was a fine art.
