The Apache web server MaxClients directive sets the limit of the number of simultaneous requests that can be supported. With KeepAlive Off this means that each element on each web page will use a separate process, and those processes will be limited to the value you choose. If you have web pages with a high number of elements this could make it so fewer visitors to the site will be able to use up all connections to the server.
Setting this parameter too low will lock clients out. MaxClients should not be set too high because your VPS has limited processes available. This value would also depend on how many processes you need for other services and how much memory your VPS has available.
If you would like some help determining the optimal setting for MaxClients for your VPS, contact email@example.com and our support staff and they can help you determine a good starting value.