[rramadass]

>Even bad estimates are better than no estimates

Absolutely not! An estimate should not be a random number but should be constrained with available data however small it might be. If you feel that you don't have enough to form a "guesstimate" do not give me a number but first work on finding the data which will enable you to form a proper estimate.

Once you give an estimate, no matter how many times you explain that it is a "guesstimate" people tend to lock on to the given number. It then becomes a real battle trying to explain the hurdles (and there are always some unknowns) while revising the original estimate. Soon mutual distrust develops between the implementation engineers (stressful and detrimental to actual execution) and the management leading to everybody losing faith in estimates. Agile/Scrum have exacerbated the problem with their short time windows and sprints. In one team that i was on, people just gave up and started quoting 2 weeks for any and every feature, trivial or non-trivial and the whole exercise became meaningless.

PS: The book "How to Measure Anything: Finding the Value of Intangibles in Business" is worth reading to get some ideas on how one might do proper estimation.