Multiple MX records with same priorty number?

I've set multiple MX records with the same priority in my zone file.
How will it work ? Will all be checked simultaneously ? what will be the pros and cons of doing that ? please
explain me how I could prioritize Mail servers ?

I got the answer from this website
MX record: Information from Answers.com

Same Priority number for MX servers

-->>When the preference numbers are the same for two MX servers, they have the
same priority, hence those two terms are used interchangeably.

To provide reliable mail transmission, the SMTP client must be able to try
(and retry) each of the relevant addresses in this list(RR records or zone db
file) in order, until a delivery attempt succeeds. If there is more than one
MX record with the same preference number, all of those must be tried before
moving on to lower-priority entries.

Basically this is basically used for load balancing, if you own
that (backup, other mail server) server too.
Otherwise there are many reson to do not assign the same priority number to MX
records, those reason are here

* * *the backup server is owned by a different company or organization
* * *the backup server does not have direct access to the primary mail * *
storage
* * *the backup server cannot determine valid recipient addresses
* * *the backup server's Internet bandwidth costs more
* * *the backup server has significantly less Internet bandwidth
* * *the backup server has a high-latency Internet connection

*
And, they will not be checked simultaneously, the DNS server is free to
carefully manipulate its balancing based on any method, including round robin
DNS, mail server load, or some undisclosed priority scheme.

Assigning the same preference value to all of the available servers provides
the same benefit and may even help avoid overload situations and thereby
increase system throughput by decreasing latency.

If you want to prioritize your MX records Then assign the lowest number to
preferred mail server and highest number to backup server.

I would make sure all of your mx records handle email the same. For example, if you have all your spam control on your primary mx and just want a secondary for failover, but it doesn't have as tight or up to date spam control, guess what? spammers notoriously use secondary or lower priority mx records for spamming. so in general I would use the same setup and adjust the priority based on hardware specs, not on which one handles spam or virus' the best.

Hi , could you explain me i did not understand that part?