What is the difference between Mapper.ProjectTo and Mapper.Map in Asp.net MVC core

When can we use Mapper.ProjectTo over Mapper.Map in Asp.Net core application? Use of ProjectTo method in Entity Framework Core, will it reduce the number of fields I query from the database to match the model if we add it in the beginning of the _mapper.ProjectTo statement? How will it reduces the query number of fields?

Instead of using this

_mapper.ProjectTo<CompareVarValdto>(_compareRepo.GetCompareDetailsByid(id))

we can use this right?

_mapper.Map<CompareVarValdto>(result)

ComapreVarValdto.cs

public class CompareVarValdto
{
    public int CompareVarValId { get; set; }
    public int CURRENT_CATEGORY_ID { get; set; }
    public int Current_LaunguageId { get; set; }
    public int Current_compareDimId { get; set; }
    public string CONTENT { get; set; }
}

Controller get method code snippet

[Route("api/[controller]")]
[ApiController]
public class ComapareController : ControllerBase
{
    private readonly ICompare _compareRepo;
    private readonly IMapper _mapper;
    public ComapareController(ICompare compare, IMapper mapper)
    {
        _compareRepo = compare;
        _mapper = mapper;
    }

    [HttpGet("{id:int}")]
    public IActionResult GetComapare(int id)
    {
        try
        {
            return Ok(_mapper.ProjectTo<CompareVarValdto>(_compareRepo.GetCompareDetailsByid(id)));
            //VS
            //var result = _compareRepo.GetCompareDetailsByid(id);
            //return Ok(_mapper.Map<CompareVarValdto>(result));
        }
        catch (Exception ex)
        {
            return StatusCode(StatusCodes.Status500InternalServerError,
                "Error retrieving data from the database");
        }
    }

compareRepo Database method

public IQueryable<CompareDim> GetCompareDetailsByid(int compareId)
{
     return _context.CompareDim.Include("Launguage");
}