I am very new to open street map and want to start mapping my area. I am finding that acquiring the address for building is very time consuming. Will OSM be effective in routing even If I do not enter building addresses? Are there any major downsides to neglecting the address?
OSM is OK for routing without addresses providing streets are not very long. In cities with regular grids where streets might be 10s of blocks long then addresses become more significant. In the longer term adding addresses to OSM is important, but for now I think we can accept that it is not high in the priorities of many mappers.
As you say mapping addresses can be quite slow. I reckon on collecting about 250 in an hour, but in locations where I only need to check a few addresses on a street to determine all the addresses. Most useful are addresses on intersections because one can interpolate between addresses within the block (and draw a line tagged with addr:interpolation=add|even|all). In Argentina where most cities have grid layouts use of these interpolation lines is standard and there has been relatively little need to survey actual addresses because the pattern is ubiquitous.
City centres or areas with lots of apartment buildings can be particularly awkward, as regular address patterns tend to be broken up. Many people take advantage of any open data on addresses to assist mapping in such places. Unfortunately availability of open data is very patchy and it’s important to be sure that the data can be used with OSM. The range of resources available depends very much on where you are mapping.
One approach is to just add buildings and other details from survey & then later use something like StreetComplete which asks for missing details on existing objects. This can break the task down, and addresses can be added incidental to doing other things.