Is there any problem with waveforms with input signals rising or falling gently?

For example, for Toshiba IC couplers TLP2355 and TLP2358, which are suitable for transmitting several-Mbps signals, Toshiba recommends drive signals making both the rise time and fall time of input signals 0.5μs or less. Should the waveform have a steeper slope compared with the case of about 0.5μs, the output potential will stay around the medium potential longer, causing output oscillation and through-current. If the input waveform has a steep slope, in some cases, the waveform must be shaped by incorporating a logic IC at the first-half stage.