Is there are any real reason to pay domain maintenance before its expiration date? I mean since you have 3 months to do it after the expiration. Thank you
You renew the domain before its expiration date to avoid the same mistake lots and lots of people have made, some of whom were unfortunate enough to no longer have it. And if you wait until 3 months after, you'll likely lose it to someone else by then.
Yes, most gTLDs and ccTLDs stop working at expiry date (so your email/website/whatever cease to be available) and very often the costs increase. If you leave it too late, you are likely to lose the domain (happens every day to peopel who ignore the renewal reminders) The rules for every domain type differ, you do *NOT* get 3 months with the majority of them. If the domain is even remotely important to you, renew it for as long as you can and as early as you can.
The post above me is correct. If you don't care about the domain anymore, there's no reason to pay anything. But if it's something you're planning on keeping, always pay your renewals on time or even a few days or week in advanced. Sometime domain registrars are nasty and if you get good traffic to your site, if you fail to pay your renewal they will resell your domain as a premium one, denying you the chance of getting it unless you pay huge fees.
I had a domain that expired by a few days, no longer than a week. I could no longer make payment for it in the control panel but out of desperation I went to the last email sent to me and clicked through on the buy now link and was able to recover it.