On a Shared IP you and a handful of other users (1-32 every group gets randomly filled up) are sharing the same IP. 

What does it mean? So lets say if one user abuses this IP in any form, any kind of disadvantages affect ALL other users assigned to the shared IP group as well. Moreover it can happen every so often often that multiple Shared IP users get moved away & blocked from a particular VPN Country. In generally speaking a Shared IP user doesnt have any guarantees being allowed to remain on a particular VPN Country - incase abuse reports come in.

Furthermore, if for example a shared IP was banned on a website, a forum, a service or whatever is the case, logically all other users sharing the same IP would be banned as well.

Being on a Dedicated IP however, assures that only you and nobody else will be assigned to this IP and therefore it's your own private IP, that being said atleast you can't be affected from other users misbehaviours. Shared and Dedicated mode have no differences in performance, all IPs are allocated to the same uplink and therefore is the speed not better or worse on either mode.

Final note about Dedicated IPs: please do not depend your entire work activities on our dedicated IP, we try our best keeping all IPs online until forever (and after 5+ years of service, fact is that in 90% of the time it works out) but due to the nature of the risky and often abuse frequent VPN business, there are still uncontrollable circumstances possible which can lead to us losing the IP one day, for example: if the server provider suspends the server, decides to remove the IP, nullroutes the IP, or whatever else may be the case. Therefore always have backup of your work and/or better additionally use a Dynamic DNS service in your setup so that incase the IP ever changes, you will be able to quickly continue your work on a new other IP.