Does using multiple switches (ordinary and non-configurable) in a LAN affect the performance of the network?
There are several possible sources of performance degradation in a switched network. Let's consider the forms they can take:
Identifying the source of any of these problems within a switch fabric can be very difficult. Since switches are Layer 2, you can't rely on the various ICMP mechanisms (path MTU discovery, ping, traceroute) to provide feedback for troubleshooting. Most of these problems are not specific to switches - auto-negotiation of duplex will devastate performance but can easily be avoided by hard-setting ports. But when it happens (and it will happen) in a switched network, it is hard to resolve.
So using switches in an appropriately designed network can be very effective. But anticipate that troubleshooting will be difficult and problems should be mitigated early by careful configuration and rigorous planning and network diagramming. Pay special attention to duplex (don't trust auto-negotiate) and MTU (don't assume defaults are sufficient). And of course, monitor performance end-to-end.