If you have only one EOI for all, then once you get an invite everything will be locked. For example, your priority is 189 but you get an invite for 489. However, you still desire to wait for 189 as you have sufficient time before lodging the visa. With separate EOIs, since the invite is EOI specific, other EOIs will not be locked. Also, some of the states desire to show commitment to them through EOI as well. Many applicants go for multiple EOIs these days as there is no restriction as such. However, it is your call.