Sections 6 through 11 of this chapter address how an altar is built and presented in a church.
6. It is desirable that in every church there be a fixed altar and that in other places set apart for sacred celebrations there be either a fixed or a movable altar.
A fixed altar is one so constructed that it is attached to the floor so that it cannot be moved; a movable altar can be transferred from place to place.(GIRM 300ff)
My parish, I’ll admit, has a movable altar. It takes about four people to budge it.
The church tells us that altars are intended to be functional, not decorative:
7. In new churches it is better to erect only one altar so that in the one assembly of the people of God the single altar signifies the one Savior Jesus Christ and the one eucharist of the Church.
But an altar may also be erected in a chapel (somewhat separated, if possible, from the body of the church) where the tabernacle for the reservation of the blessed sacrament is situated. On weekdays when there is a small gathering of people Mass may be celebrated at this altar.
The merely decorative erection of several altars in a church must be entirely avoided.
The altar is a focal point, identifiable even above devotional elements such as a crucifix or a tabernacle:
8. The altar should be freestanding so that the priest can easily walk around it and celebrate Mass facing the people. ‘It should be so placed as to be a focal point on which the attention of the whole congregation centres naturally.’(GIRM 299)
This begs the question: if this is true, how can the altar be obscured, even partially, by clergy or decorations such as candles or flowers? As for the first statement above, the importance is less the direction the priest faces (which I think should be irrelevant) and more on visibility of the elements and the rituals associated with them.