There's not much of a reason NOT to have a sitemap. It's a great benefit for you and enabling robots to see your whole site. TIP: place a link to your sitemap in your footer, so if a spider comes crawling one of your deeper pages, it'll find the rest of your site and your indexing will be stronger.
no its not an necessary it depend on you if you use site map then search engine spiders can easily find your site constants and its helps you to get more visitors
No it is not needed but google would like it So if you want to be in googles good books and tick all their boxes you should get one If not then you don't really need to bother
Its not necessary to have a sitemap . If you want to google crawl your all the pages on the site then you do need the sitemap. anyways its always good to have a sitemap which could be of help to visitors also .
Yes, submitting sitemap is very important, because it let the crawler to access your site contents. Try to Re-submit your sitemap if you make any changes or add some new contents to your site.
We use gSiteCrawler for all our Sitemap needs and we find that sites with them do much better. Just keep them current and updated. Also, you should have a Google Webmaster Tools account set up for your site. This give you Google feedback on what's going on with your site. It removes the guess work.
Sitemap is not a mandatory thing to have for a website, but if you have a big website, you should have it to get better indexing in the search engines like Google, yahoo! and bing
Place a link to your HTML sitemap (or the HTML version of the same sitemap). I am not pretty sure if you link your XML sitemap SEs will follow the entries from it during a regular crawl. For me the biggest advantage of the Sitemap is that if you log in to Google Webmaster Tools you can see how many pages of yours got indexed, so you follow the whole indexing process.
It is useful to get indexed very quickly. If it is XML. and you can aslo helps visitor through it. so they can easily find the pages where the want to go.
Creating sitemap is the way to tells the Google about the pages / new pages and Title changes! The only drawback is, you can't tell the Google for the content changes on the website till the Google crawl in some days and give you better listing or dropped your listing!